This invention relates generally to sprue gated injection molding apparatus for five layer molding and more particularly to such apparatus having two melt passages extending from a common melt source with one of the melt passages having a control valve to control melt flow to a central melt channel in each heated nozzle.
Multi-cavity injection molding apparatus for making five layered protective containers for food or preforms or parisons for beverage bottles are known. Two layers of a barrier material such as ethylene vinyl alcohol copolymer (EVOH) or nylon are molded between two outer layers and a central layer of a polyethylene terephthalate (PET) type material. For instance, U.S. Pat. No. 4,717,324 to Schad et al. which issued Jan. 5, 1988 shows apparatus for sequentially injecting first the PET, then the barrier material and finally the PET again through two different melt channels. While this is satisfactory for some applications, sequential molding has the disadvantage of a relatively lengthy cycle time.
As seen in U.S. Pat. No. 4,990,301 to Krishnakumar et al. which issued Feb. 5, 1991, U.S. Pat. No. 5,131,830 to Orimoto et al. which issued Jul. 21, 1992, and U.S. Pat. No. 5,141,695 to Nakamura which issued Aug. 25, 1992 injection molding apparatus is also known to simultaneously inject multi-layered products, but this apparatus has the disadvantage of requiring a separate melt source and a separate valve for each melt passage.